code: def forward(self, agent_qs, batch):
      return torch.sum(agent_qs, dim=2, keepdim=True)
  
file_path: ray/rllib_contrib/qmix/src/rllib_qmix/qmix/mixers.py
imports: import numpy
  from ray.rllib.utils.framework import try_import_torch
label_desc: Use image node_id 2 for calling the VDNMixer obj's underlying member method code with example usage: obj.forward(agent_qs, batch) and returns: torch